Subsurface safety valves are used for emergency well control. A common design has a flow tube that is actuated by a hydraulic control system from a surface location. In a single control line system the application of pressure to the single control line has the effect of shifting the flow tube into a closure member that rotates 90 degrees to a position behind the flow tube as the flow tube advances. This closure member is known as a flapper. A closure spring is provided to act against a piston that actuates the flow tube. In SCSSVs (surface controlled subsurface safety valves) for Deepset application control line system there are in some instances a compressed gas chamber, atmospheric chamber or other components in the safety valve that acts on the piston in the same direction as the closure spring to offset the pressure from the liquid column in the control line so that the closure spring need only to act against the weight and friction forces acting on the flow tube. When the flow tube is raised by the closure spring the flapper can pivot 90 degrees to a seat and prevent flow from coming up the wellbore for control.
There is a reluctance of operators to use single line valves with pressurized gas chambers to offset control line hydrostatic because there is a risk of loss of gas pressure that could make the valve inoperative. One way around the use of pressurized gas chambers is to use dual control line safety valve control system where the hydrostatic pressure in one line is offset by the hydrostatic pressure in an adjacent line. Two line systems cost more to install and take up more space in a crowded annular volume that must be shared with umbilical assemblies that are used for power, signal, injection and other functions downhole.
In shallow set SCSSV applications a landing nipple is provided either above or integral to the safety valve so that if the original safety valve fails for any reason, what is called an insert safety valve can be landed on the nipple with a wireline after a wall opening is created with a penetration tool to provide access to the control lines that are associated with the landing nipple. There are conflicting demands when providing the option for an insert safety valve particularly in deep water applications where the regulations require the insert safety valve to be below the sea floor which can be thousands of feet below the surface water level. Such depths would normally require the use of a compressed gas chamber, atmospheric chambers or other means to offset the hydrostatic pressure if the insert valve was to run on a single control line. On the other hand if the insert valve were to run on a system with two control lines there can be space problems in view of the fact that the original control valve has at least one control line extending to it to make it a total of at least 3 control lines going to the surface.
In the present invention a way to have dual use of a control line for two different safety valves allows the line count to be reduced to two lines so that the insert valve can operate with a balance line and without a need for a pressurized gas chamber, atmospheric chambers or other means. The original safety valve would have a single control line and an opposing gas chamber atmospheric chambers or other means for the hydrostatic pressure. The single line to the original safety valve can be run into a second port on a landing nipple above so that when the second wall penetration happens in the landing nipple, the operating line for the original valve becomes the balance line for the insert valve. The first wall penetration in the landing nipple allows access to another line that terminates at another connection on the landing nipple. Thus, when the insert valve is latched into the landing nipple there are two lines connected to operate it with the balance line to the insert valve having previously served as the operating line for the original safety valve. Systems with an original valve having dual lines can still benefit from the present invention with the line count reduced to three lines total instead of what would otherwise have been four lines to make the original valve and the insert valve above it both operate without pressurized gas chambers atmospheric chambers or other means to offset control line hydrostatic. These and other aspects of the present invention will become more readily apparent from a review of the description of the preferred embodiment and the associated drawing while recognizing that the full scope of the invention is to be determined from the appended claims.